By way of example, currently the demand for decontaminated food products is increasingly higher, as demonstrated by the recalls of products contaminated with listeria, and the costs generated are often enormous.
The cost for obtaining quality is currently a hindrance that European Community regulations are in the process of correcting by requiring increasingly substantial guarantees.
Being able to propose “pasteurized” products instead of “sterile” or at least “decontaminated” has become a requirement in the worldwide market.
The targets are: enterobacteria of the Escherichia Coli type, total flora, yeasts and molds.
In the production method, the major actors in the market are for the moment still in “westernized” countries. They purchase herbs and spices produced in the various countries of the world, and the latter, often contaminated, must then be “debacterized”. Indeed, the steps of drying are often carried out directly on the ground in some countries, for economical reasons.
Currently, there are various technologies available on the market that make it possible to decontaminate the products in various forms.
Irradiation, microwaves, ionization, ozone, gases of the polypropylene oxide type, depositing decontaminating substances, generally speaking all of the solutions other than water vapor are not solutions that have a future, for the moment, because they are subject to specific markings on the final packaging which is a genuine hindrance to marketing (a product decontaminated via irradiation is harder to sell).
Other systems using steam are differentiated into two sub-categories:
“batch” systems of the autoclave type: batches are treated unitarily, which allows for perfect traceability but which requires high manpower costs. These systems are used extensively in the pharmaceutical industry.
Continuous systems.
The fundamental parameters in decontamination via steam are:
The temperature of the product
The method of transport of the product
The temperature of the steam
The passage time of the product
The quantity of steam used
Indeed, a passage time of a few seconds at a high temperature can have the same effect as a time of 3 minutes at a lower temperature. But the product can be altered by the temperature. The quantity of steam used will remove essential oils and flavorings from the product, which alters the final quality of the product in terms of color as well as taste.
The method of transport of the divided solids and the method of treatment and heating greatly affect the cost of the installation, the quality of the treatment and the quality of the final product.
The compromise between what the customer can accept in terms of color, taste, and the level of contamination with regards to the cost of the treatment provides the technical-economical compromise to be found.
Decontamination must be as thorough as possible, in such a way as to achieve the acceptable levels of contamination, without degrading or destroying the organoleptic characteristics of the products, having the smallest possible degree of alteration of the products in terms of color and taste; using the most economical method of heating possible and a method of transport which makes it possible to satisfy all of these imperatives.
A continuous decontamination unit is comprised of a product supply, a debacterization unit, a cooling drying unit and a packaging unit.
The system for supplying the product is often an option available to the users.
The debacterization via steam portion obviously requires steam. A boiler to produce this steam is an option that few users choose; indeed industrialists in the agro-foods industry are generally equipped with steam in their factories. However, vigilance must be taken concerning the fact that a unit requires regulated steam and also often superheated between 100 and 140° C. This implies an option with a superheater.
Then, also, the portion concerning extracting the steam to the exterior must also be provided. The latter will in general also be used for extracting the cold and dry air used in the cooling portion which reduces issues concerning condensation.
Customers often have in their factories extractions systems nearby that they can connect to.
When the product exits the debacterization unit it is hot and wet. So that it is not immediately recontaminated by the air it is imperative to dry it and cool it.
The product is then brought to the cooling-drying unit.
That is why having cold, dry and filtered (not contaminated) air is required and often the users are equipped with this. These installations are very expensive and greatly affect the cost of the installation.
The cost largely depends on the demand from the user: what temperature of the product in relation to the exterior temperature can be accepted at the exit of cooling, keeping in mind that the last 5° C. are the most difficult to obtain and that the difference in relation to the ambient conditions is often substantial (in Malaysia, the temperature is 30° C. and the humidity is 95%, in Greece 35° C. and very dry. The imperatives are different).
When the product is dry, debacterized and at a temperature which allows it to be packaged without immediate recontamination it is stored or packaged. A “big bag” bagging system, simple and inexpensive, is a commonly proposed option.
The main systems known on the market consist in creating:
a fluidized bed (transport by vibrations) moving the particles on a metal plate pierced with a multitude of holes and the steam is used to heat the particles and debacterize them.
Advantages: high degree of homogeneity of the treatment and possibility of treating all the sizes of particles but the price of the installation is very expensive and there is a lot of steam which substantially degrades the products.
A system is also known that consists in using a stainless steel tube wrapped as a spiral around a tower heated via the Joule effect, with this tower subjected to a vibration which makes it possible to raise the product. Steam is injected from one side of the spires and extracted from the other.
Advantages: approximately 10 times less steam is needed than previously because the particles are heated by contact on the tube, the steam is used only for the debacterization. But the disadvantage resides in the very high price for small capacities because this makes use of electrical power, powders are not sufficiently decontaminated, caking at the input and output i.e. in the cold zones, and the vibro-fluidized bed of the tube does not guarantee homogeneity of the treatment.
A third known system consists in using a worm screw in a trough, with both heated by the Joule effect, the screw causes the product to move forward. Steam is injected all along the trough, in order to decontaminate the product.
Advantages: approximately 10 times less steam than in the first case as the particles are heated by contact with the screw and the trough, but the price of the installation is substantially affected by the electrical power. The space between the trough and the screw leaves a bed of untreated product which limits the effectiveness of the treatment by not guaranteeing its homogeneity.
The study of concurrent systems shows that electrical power should not be used which requires the use of expensive electrical transformers.
The transport system must not be carried out by a screw as it does not guarantee homogeneity for the treatment.
The vibrating tower is too expensive to be used as such.
The particles have to be heated (before debacterization) other than with steam otherwise the products are degraded.
In fact:
The transport must be carried out via a “converted” fluidized bed.
The steam has to be superheated in order to decontaminate faster
The heating of the fluidized bed shall be carried out by off-the-shelf electrical resistances.
The system must be able to treat all particle sizes including powders.